Background Several observational studies have demonstrated an association between obesity and asthma. Studies evaluating exhaled nitric oxide levels and obesity have revealed that a higher body mass index (BMI) is associated with elevated exhaled nitric oxide levels. Airway inflammation using sputum cell counts has not been assessed in obese patients with airway diseases.
Objective The primary aim of this study was to determine whether obesity (based on BMI) is associated with eosinophilic or neutrophilic bronchitis.
Methods The results from a database of induced sputum cell counts were compared with BMI and analysed using correlation statistics, regression and parametric and non-parametric analysis.
Results Seven-hundred and twenty-seven adult participants with an equal number of sputum samples were included in the analysis. BMI varied from 14.5 to 55 kg/m2. Sputum total cell count (mean±SD: 12.9 × 106 cell/g±21.5), eosinophil percent (median; min to max: 0.3%; 0–89.0), and neutrophil percent (mean±SD: 63.5±26.6%) were within normal limits. Participants with asthma had a higher percentage of sputum eosinophils than those without asthma (P=0.01). However, there was no difference in the total or differential cell counts among the obese and non-obese participants, when the data were analysed according to BMI category, gender, dose of inhaled corticosteroid, and presence or absence of asthma.
Conclusion In this large sample of adult asthmatic and non-asthmatic participants, there was no association between BMI and airway inflammation measured by sputum cell counts. Other mechanisms to explain the relationship between obesity and asthma will need to be explored if this association is to be better understood.